Transmitter



March 8, 1932. F. H. KROGER 1,848,133

TRANSMITTER Filed July 5, 1928 INVENTOR FRED. H KROGER ORNEY Patented Mar. 8, 1932 1 rain) 1:. naoena, or new YORK, N. Y., Ass'I 3 TRANS,

' qApiiHcatlont filed July 5,

in particular to transmitters for-mobile use operating at 100 meters or under.

In certain classes of commumcat'on where 5 wavelengths belowfl100 meters are used, 1t is desirable to be able to change the transmitters wavelengths quickly a definite arbitrary amount while still remaining n the wavelength band assigned for this type of com-.

'municat'ion. An illustration ofthis practice is'that of the present marine communication system.

"The short wave transmitter :used in this type of communication which are generally iconstructed without frequency controlmeans:

to these frequency variations, at times, di'fii cult to copy. Particularly is this so intransmitters designed for mobile use. 7 Briefly and in its broadest aspect the obaojectof this invention isto providea transr.

mitter. in which frequency control other than that obtained by the oscillator and its associated circuits is not necessary and which includes means for reducing the eifect at the "receiver of the varying frequencies-transmitted.

This object is-attained by the use of a master'oscillator which is arranged in construction and circuit together with the character of plate'and filament supplies; within practical'limits to give constantfrequencies as established by the oscillator tube or tubesand associated tuned circuits; The master oscillator excites continuously the grid ofan amplifier; The amplifier preferablyconsists' of two tubes which'are arranged in a selfrectifying circuit and with which 'is"as 'so-' ciated a radio frequency tank circuit'from tennaor other load circuit; The plates of This 'invention relates to transmitters and.

Designing 1 which the'energy'-may be supplied to anr'an- GNOB 'roRAn'ro coaroaarron A coaroamrron ornnLA aRE Mrr'rna 1923. Serial 110.290378,

tlie amplifier tubes are supplied from the secwhich is fed by an alternating current generator. 1

Keying of the transmitter may be done in] any convenient manner, 7

The formofenergy delivered to the tank circuit from the output'cir'cuits of theam'plifier is of varying amplitude and of a fre 'qu'ency double that of the alternatingcurrent generator while the frequency of the vcarrier l Wave is determined by the master oscillatorg The tank circuit of the am'pllfier ln'the sini-n pler arrangeinent supplies the energy to the antennaor transmission line 'or to other work circuit.

The form of energy obtained from a tran t tres-5;;

or AMERICA,

Vondary vof a transformer the primary of' mitter constructed in accordance with my in- Y vention gives a pleasing musical effect in'the receiver whenheterodyning and 1s of a na- 'predominent after heterodyning a carrier wave of practically constant amplitude are now in the background due to the predomi natin'g of the frequency of modulation. One advantage to begained by the use of tune easy to pick up when tuning. The many, variations'of frequency which would appear a transmitter constructed in accordance with 1 my invention is that thehigh voltage direct plates of the amplifiers in transmitters of this I type is replaced by an alternating current current generator usually used to supply the generatorthereby materially decreasing the I cost of the apparatus.

Another advantage to be gained by the use ll of a transmitter constructed in accordance with my invention is that the high voltage CllIGClZ current generator generally. used in transmitters of this type is replaced by an alternating current generator of low voltage,

thereby'materially increasing the reliability of the apparatus.

V A' further advantage to'be gained by'the useof a transmitter arranged in accordance with my nvention isthat control means such 'it'ycf signals.-

'use of a transmitter constructed in accord Anl'added adva tage to begainea by t e as for instance a crystal control maybeomit tedfwithout appreciable sacrifice in readabil' ance with my invention is that transmission on the shorter wavelengths may be carried out by apparatus permitting a convenient change in wavelength.

An additional advantage to be gained by my novel transmitter is that the radiation therefrom provides two side bands ad acent to the carrier Wave which are helpful in reducing fading at the receiver.

, Other objects and advantages will become apparent from the specification and therefrom when read in connection with the accompanying drawings in which;

Figure 1 illustrates the at present preferred form of the invention; while Figure 2 is a curve showing the current oscillations in the tank circuit.

Referring to Fig. 1 of the drawings the radio frequency carrier wave is generated by a master oscillator of any standard type, which for purposes of illustration has been shown as an oscillator of the Hartley type. This oscillator M.O. consists of a vacuum tube oscillation generator 3, the anode of which is supplied from a high potential direct current source 1 through a radio frequency ClIO kB COIl 2 the purpose of which is to prevent oscillations at radio frequency from passing through the current source. The frequency of the oscillations generated by the master oscillator is determined by the oscillation circuit 5 which consists of a condenser 9 shunting an inductance 10 a portion of which inductance is common to the grid cathode and anode cathode circuits of the master oscillator 3. The grid cathode circuit is completed from the grid through a grid leak 6 shunted by a condenser 8, through a portion of the 1nductance 10 to the cathode. The amount of the inductance 10 in this circuit depends on the position of the point at which the conductor 7 connects this inductance to the cathode. The grid leak 6 shunted by the condenser 8 assures proper bias for the grid of vacuum tube 3. The anode cathode circuit 1s completed from the anode through a blocking condenser 4: a portion of the inductance l0 and the conductor 7 to the cathode of the tube. The inductance 10 being common to the anode and grid circuits provides the required feedback coupling inductive and conductive between said circuits to set up sustained osclllations in the anode cathode circuit.

This oscillation generator which has been described merely for purposes of illustration it being understood that many alterations in the arrangement thereof can be made without departing from the spirit thereof, will not produce oscillations at constant frequency but will within reasonable limits produce oscillacarrier wave is required thereby gaining all the advantages to be drived from a constant frequency generator while still retaining the advantages to be obtained by maximum simplicity of structure and ease in change of frequency of the oscillations produced.

The oscillations generated by the above described master oscillator are led through a coupling condenser 12 to the grids of an amplifier ofthe push-pull type by means of a conductor 11 variably tapped to the inductance 10 a portion of which is in the amplifier grid cathode circuit which is completed of the choke coils 23 and 24 is to keep high frequency oscillations from being set up in the transformer secondary 25. The midpoint of the secondary winding of the trans-- former is grounded at G. The cathodes of the tubes 13 and 14 are connected to ground through a conductor 17 thus completing the anode cathode circuit for the modulating cur,- rent. The grids of the amplifier tubes 13 and 14 are grounded through a choke coil 15 the purpose of which is to exclude radio frequencies from the low frequency circuits, and a high resistance 16 the purpose ofwhich is to provide the proper potential on the grids of 13 and 14. The output circuit of this amplifier includes two symmetrical portions comprising conductors connecting. the respective anodes of the amplifier tubes 13 and 14: through two blocking condensers 18 and 19 with a conductor 20 connecting the grounded tank circuit 30 to a point between the condensers 18 and 19. This output circuit is completed through the grounded conductor 17.

The tank circuit 30 comprises an inductance 22 shunted by a condenser 21 thus forming an oscillation circuit tuned to the desired frequency. Energy may be taken from the tank circuit by means of a pair of conductors variably tapped to the inductance 22 of the tank circuit and designated output in the drawings.

Although for purposes of illustration 1' have shown a pair of conductors for taking the energy from the tank circuit, I do not 7 limit myself thereby as the energy may be taken from the tank circuit in any known manner to supply anywork circuit as for inmesses stance by inductive, or capacitive coupling to an antenna circuit. r

The transmitter may be keyed means.

of a key 27 in the circuit of'the alternating current generator 28.

The opposed potentials applied to the anodes of the tubesof the self-rectifying amplifier by the secondary of the alternating current transformer 25,26 will causedirect current to flow alternately in the direct current anode cathode circuits of the tubes 13 and 14. The sum of these currents flowing in the respective anode cathode circuits of the tubes 13 and 14 would if plotted with respect to time be represented by a series of direct current impulses the frequencies of which are double the frequency of the alter up in the tank circuit in response to the'effect of the voltage of the'oscillations of the master oscillator on the input circuit of the amplifier and to the modulating effect of the alternating potentials applied to the anodes of the amplifiertubes. In this figure 31 in-- dicates the oscillations set up in the tank circuit. The frequency of these oscillations is determined by the tuned impedance 30 and is to obtain maximum amplitude variation equal to the frequency of the oscillations'impressed on the input circuit of the amplifier by the master oscillator. As shown in the drawings these radio frequency oscillations vary in amplitude from zero to maximum and back to zero at double-the frequency ofthe generator 28 the amplitude of these radio frequency oscillations being a function of the amplitude of the potentials applied to the anodes of the tubes of the self rectifying am- If rectification of the alternating current fed to the amplifier anodes by thegenerator 28 is not complete, modulation of the radio frequency oscillations in the tank circuit will not be complete but will be substantially as indicated by the dotted line 32 in Figure 2 of the drawings.

To briefly describe the operation ofmy novel transmitter, the oscillations" generated by the master oscillator are fed to the input circuit of the amplifier by the conductor 8 and are modulated therein by the low frequency anode supply provided by the genera-/ tor 28 and rectified by the novel amplifier arrangement. These low frequency oscillations will produce in the direct current anode cathode circuit of the amplifier rectified pul-. sations of double the frequency of the oscilat on rprevi by hegenera or 2.8- flhe e t ons pr duced in he radioif quencyioutp circl'ii v of the ampli ier in response :to the voltage changes applied ;to the ;grid .jcath0de circuit thereof by the oscillations from the maste s i t R dio frequency current os lla ion lare set up inst e tank circu tf om Which-they-may b utilized in a Wendi-mowing m nncn; I

I have found that when the generator 28- is operatedat a frequency of 500 cyclesper s co d th n t ai ed in the receiv r .aby

l eterodyni ng is easy to listen to, and that even though the frequency of :the master oscillator varies the musicalnote.will; stillbe present in the receiver andthoughsomewhat mushyTwilLalwaysbe readable.

Although for purposes, of illustration :1

ferred form of -.my invention {and the eper-a: tion thereof I do not wish to :limit myself thereby exceptas marked out in the claims reto ppended i .s

' 1. An apparatus forsignalling at radio frequenoies'the combination of an amplifier tubes having input and output. elements arranged m. a self-rectifying circuit including an output circuit and an inputcircuit, a tank haveshown and describedthe at present ,pr,e

system comprising a plurality of thermionic circuit in said output circuit, means for op-' positely supplying low frequency alternating 9 current potentials to the anodes of said tubes including a transformer secondary winding the midpoint of which is connected to the grids of said tubes, keying means associated with said supplying means,cand means for supplying high frequency oscillations to the input circuit of said amplifier.

2. In apparatus for generating high frequency. oscillations the combination of an.

amplifier system comprising a pair of tubes each having an anode grid and cathode elec trode, an input circuit connected between the grid and cathode electrodes of said tubes,

an output circuit including capacitive means for coupling said anodes together and to a tank circuit'comprising a tuned impedance, associated with said anodes and cathodes, a

low frequencyalternatmg current generator associated with the primary circuit of a transformer having a secondary symmetrically tapped and grounded to the cathodes of said tubes, means including a high resistance and a choke coil for connecting the mid-point of said secondary to the grids of saidtubes, means including impedances for connecting' each of the outer ends of said secondary to the anodeof one of said tubes, a high frequency thermionic generator having coupled input and output circuits and means for connecting the input circuit of said amplifier to the output circuitof said thermionic oscillation generator.

3.- In an arrangement for producing substantially constant high frequency oscillations, the combination of an'amplifier' system comprising a plurality of thermionic tubes having input elements including a control electrode, and output elements, means for connecting a source of high frequency oscillations between the input elements of said tubes, said connecting means including a capacity, a high frequency output circuit including a pair of condensers connected in series between theanodes of said tubes and a tank circuit connecting the midpoint of said condensers to the filaments of said tubes, a source of alternating current at audible frequency, a transformerhavingaprimarywinding connected with said source, and a secondary Windinghaving its terminals connected through inductances to the anodes of said tubes, an inductance and a resistance connecting the electrical midpoint of-said trans former to the control electrodes of said tubes, and keying means in series with the primary winding of said transformer.-

FRED H. KROGER. 

